Ocular dominance column
Ocular dominance columns are regions of neurons in the visual cortex that synapse with axons carrying transduced signals from either the left or right eye. The columns span multiple cortical layers, producing a striped pattern when the deeper levels are stained.
Prior to birth, monocular transduction pathways are already established through a process known as Hebbian learning. Spontaneous retinal activity in one eye of the developing fetus leads to neuronal depolarization. Synapses that receive multiple inputs are more likely to propagate the signal, whereas errant connections will not be sufficient to trigger another action potential. Post-synaptic neurons that depolarize become permeable to calcium ions, if glutamate has been released by the pre-synaptic axon terminal. Calcium’s entry leads to a chemical process that strengthens the synapse, making it more likely to survive than other connections.
In a normally-developed visual system, the area of dominance columns for both eyes is the same, and each cortical cell responds to visual input according to its column. Monocular deprivation during early life prevents this balance from developing, and the non-deprived eye assumes control of nearly all cortical cells. These effects were identified by Torsten Wiesel and David Hubel, neuroscientists at Harvard Medical School, through studies on cats.
- Kolb & Whishaw: Fundamentals of Human Neuropsychology, 2003